The airway surfaces are covered by a thin layer of liquid (ASL) consisting of a mucus layer residing on top of the periciliary liquid layer (PCL). The mucus layer traps debris and pathogens deposited on the airway surfaces, while the PCL layer provides a low viscosity liquid for efficient ciliary beating and functions as a lubricant layer. CF airway epithelia exhibit dysregulated epithelial Na+ channel (ENaC) function and absent CFTR CI- channel function, which results in hyperabsorption of Na+ and osmotically induced water absorption. We hypothesize that the net effect of Na+ hyperabsorption is to (1) deplete the PCL volume, (2) collapse the mucus layer onto the cilia, (3) slow both cilial and cough-dependent mucus clearance, (4) leading to accumulation of mucus plaques and plugs that are a nidus for bacterial colonization. While this hypothesis has been supported by data from in vitro experiments, the lack of an animal model has limited experiments to test this hypothesis in vivo. To test the hypothesis in vivo, we have generated transgenic (TG) mice that use the CCSP promoter to over-express the individual ENaC subunits (a,b,g). Preliminary data indicate that over-expression of the b subunit leads to an elevated rate of airway Na+ absorption, a decrease in PCL volume, marked mucus accumulation and plugging of the airways, and approximately 50% pup mortality by day 28. We propose four Specific Aims to study mice over-expressing b ENac as well as other ENaC subunit combinations.: Aim 1. Mice will be characterized with respect to survival, weight gain, pulmonary function tests, and histological/bioelectrical study of airways. Aim 2. The volume of the PCL/ASL, rate of volume flow, PCL ionic composition, mucus % solids and mucociliary clearance will be measured. Aim 3. We propose bacterial infection studies (P. aeruginosa) on the b TG mice, to generate insights into the initiation of inflammation and infection as well as information on the genetic and morphological changes in the bacteria in response to the host. Aim 4. We will test therapeutic agents aimed at blocking ENaC and dissolving mucus in airways of neonatal and adult b TG mice. Thus, our mouse model will be key in fostering translation of basic science to clinical application in a disease for which we now, for the first time, have an animal airway model.